Electronic cards such as modem cards, Local Area Network cards (LAN cards) and memory cards are widely used and developed toward minimization. The common standard specifications of electronic cards comprise for example PCMCIA cards, Compact Flash cards (CF cards), secure digital cards, etc. In addition, some new standard specifications are still in development. The contents associated with these specifications are somewhat different. However, the packaging structures of these electronic cards are basically identical. Such packaging structure comprises a case for encapsulating a printed circuit board (PCB). The external surface of the case should be electrically conductive and comprises a ground terminal. After an electronic card is inserted into a slot of an electronic device, the ground terminal will be electrically connected to the system reference of the electronic device for grounding.
The packaging structure of the electronic card needs to provide sufficient mechanical strength and electrical properties, which should meet certain standards required. Moreover, it is necessary to produce these electronic cards on a large scale and with low cost. According to the conventional packaging process, a printed circuit board is firstly clamped by a plastic frame, and then a top metal cover and a bottom cover are riveted by a clamping tool. Afterward, the printed circuit board and the plastic frame are encapsulated. Since the metal covers and the plastic frame of this packaging structure are not tightly coupled, the metal covers are easily loosened or fallen off when an external force or a deflection force is exerted. Moreover, the packaging structure formed by means of riveting has poor mechanical strength, and thus results in deformation of the metal cover.
Another process for combining the metal cover with the plastic frame comprises a viscose binding process or an insert molding process. By using such process, when an external force or a deflection force is exerted on the electronic card, the bonding portions between the plastic frame and the metal cover are readily separated due to the insufficient force. Especially, when the insert molding operation is performed to combine the metal cover with the plastic frame, the required molds should be previously established. Therefore, the cost is very high. Subsequently, the metal covers and the molds are precisely aligned with each other. Afterward, plastic material is inserted into the molds so as to combine with the metal covers. Such insert molding process is time-consuming, labor-intensive and costly. The insert molding process has been described, for example, in U.S. Pat. Nos. 5,379,587, 5,475,919 and 5,490,891, and Taiwanese Patent Nos. 482305, 471673 and 549688.